1. Field of the Invention
The present invention relates to an image processing apparatus for extracting an image portion from a two-dimensional image.
2. Description of the Related Art
Recently, two-dimensional images produced by imaging objects by using imaging apparatuses such as scanners, digital still cameras, and video cameras are stored into storage media as image signals of binary digital data signals. Then, the two-dimensional images stored in the above-described manner can be electronically processed by employing electronic appliances such as computers.
To electronically process a two-dimensional image in the above manner, for instance, a desired image region within the two-dimensional image is selected so as to be extracted by an operator of an electronic appliance. At this time, for example, this operator manipulates a mouse in such a manner that a contour of the desired image region within the two-dimensional image is traced by way of a mouse cursor movable within this two-dimensional image in conjunction with the mouse. As a result, this desired image region can be designated. In this designating manner, when a desired image region owns a complex contour shape, it is difficult for the operator to trace the contour correctly or accurately. As a consequence, a lengthy operation time would be necessarily required so as to accurately designate the desired image region. Also, very cumbersome process operation would be given to the operator.
As one prior art related to a two-dimensional image processing technique, an image editing apparatus is described in Japanese Unexamined Patent Publication JP-A 1-175076 (1989). In the prior art image editing apparatus, an operator of this image editing apparatus first designates an envelope line which surrounds a desired image region within a color natural image. Next, among coupled regions in which pixels having similar colors are coupled to each other within the region surrounded by the envelope line, a coupled region having an area larger than or equal to a predetermined ratio within the above region is removed from the region within the envelope line. Thus, the remaining region is cut out. In this image editing apparatus, it is desirable that the coupled region will constitute the background of the desired image region. However, in the case that this background is constituted by coupling a number of regions wherein completely different colored pixels are coupled to each other in a small number, the dimensions of the respective different-colored coupled regions are decreased. As a result, since these different-colored coupled regions can be hardly removed from the region within the envelope line, it is practically difficult to cut out only a desired image region.
Also, as another prior art related to a two-dimensional image processing technique, an image clipping apparatus is described in Japanese Unexamined Patent Publication JP-A 5-216992 (1993). In this conventional image clipping apparatus, an image to be processed is divided into a plurality of regions, depending upon the similarity of features of spatial frequencies. Then, an operator of this image clipping apparatus designates a region containing a desired image region from the divided regions. Subsequently, based upon the color distribution within the designated region, the image region is extracted. In this image clipping apparatus, the image is divided on the basis of the spatial frequencies. However, the desired image region is not always involved in a single divided region. Thus, the operator is required to designate a plurality of divided regions, resulting in cumbersome operation. In the case that the feature of the spatial frequency of the desired image region is similar to that of the remaining region within the image to be processed, the divided regions may excessively become larger than the desired image region. In this case, it is difficult to extract the desired image region based upon the color distribution.